a tunnelling landmark

Map of Eupalinos Tunnel
(Ernst Fabricius 1884)

In 1992 UNESCO declared the area of Eupalinos Aqueduct a World Cultural Heritage site.

The monument is a milestone in tunnel engineering since the engineer of that time think innovatively and deviated from the classical, for that period, method of tunnel construction (the qanat method). Eupalinos used mathematics and geometry not only to align the excavations before they met, but also to “manipulate” the alignment of the tunnel in order to avoid adverse geological conditions. Mutatis mutandis, the basic principle behind the method of Eupalinos, has been used again long after the Renaissance of Europe (early 18th century), and it is still in use in modern tunnelling.

The Eupalinos Tunnel is considered as one of the most important engineering achievements of antiquity. It's a 1036m long tunnel in Samos Island, Greece, built in the 6th century BC to serve as an aqueduct and therefore supply fresh water from Agiades spring the city of Samos (Pythagoreion). The Eupalinos Tunnel is an engineering feat of outstanding importance since it was the first time in the history of mankind that anyone had ventured to undertake a project of that magnitude with no similar reference. The Engineer Eupalinos built a tunnel under a mountain by starting to dig, simultaneously, from two portals diametrically opposite. All applied measurements using maths and geometry are of outstanding precision. Moreover, all evidence indicate that Eupalinos was ready to apply a solution for every difficulty that arose, due to unfavorable ground conditions that were partly encountered, as well as that he had the courage to bring his highly difficult project to a successful end. Eupalinos worked as a modern engineer 2500 year ago.

The Eupalinos Tunnel was used for over 1100 years (up to the 7th century AD) until it was abandoned in the Byzantine period, during which it was used for long periods by the Samians as a refuge. The tunnel offered unique protection for the people against pirate invasions. Fortressing walls were built inside the tunnel just after its south entrance portal.

Archaic (left) & Roman (Right) tunnel linings

Herodotus
(~ 481–425 BC)

Herodotus (481-425 B.C.) is the first historian who makes an enthusiastic reference to the monument. He names Eupalinos, son of Naustrophus, born in the city of Megara as the engineer responsible for designing and building the ancient project. He also describes the method of construction that makes this monument unique: “…One is a tunnel, under a hill one hundred and fifty fathoms high, carried entirely through the base of the hill; its excavation started from two portals…”. It is the first tunnel known that has been built under a mountain starting to excavate it from two diametrically opposite portals using mathematics and geometry for keeping it aligned.

﻿"No monument similar to the Eupalinos aqueduct exists in the science of archaeology﻿"

(Kienast, 1995, German Archaeological Institute)

The Aqueduct of Eupalinos has a total length exceeding 2,5 km involving a bored tunnel 1036m long, which consisted of a corridor having internal dimensions 1.80x1.80m and of a ditch 0.60m wide. The depth of the ditch ranged from 4.0m in its northern section to 8.9m in its southern one, to ensure gravitational water flow. The maximum overburden of the tunnel is ~ 170 m below the summit of the mountain and its elevation is 55m above sea level. The tunnel was hewn out simultaneously from both sides, and two crews of stonemasons, working with hammers and chisels, met with almost no deviation. It is estimated that 8-10 years were required to complete the project.

The aqueduct started from the Ayiades spring, the “great spring” according to Herodotus, where water was collected in a rectangular reservoir covered by stone slabs. The water was transferred from the reservoir, which supplied 400 m3 per day, through an underground clay pipe (length: 890 m) to the northern entrance of the tunnel. It was carried from the tunnel’s southern exit to reservoirs and fountains in the ancient city via a pointed underground built channel with manholes at intervals. The central section of the aqueduct, consists of the “Eupalinos tunnel” within with the water was channeled through clay pipes, parts of which are still visible.

Victor Guerin, a French archaeologist who searched for the “great spring” of Herodotus, was the first person who discovered the first 400m of the aqueduct, from the Agiades spring, in 1853. However, it was the monk Kyrillos Moninas, in 1882, from the nearby Agia Triada monastery who succedded to discover the south and north entrances of the main tunnel. In 1884, E. Fabricius, an archaeologist of the German Archaeological Institute in Athens (DAI), visited the island and surveyed the tunnel up to the point that could be visited at the time. In 1971 U. Jantzen, Director of the DAI, succeeded after long preparations to excavate and research the tunnel (1971-1973).

how did Eupalinos keep the tunnel aligned?

No one knows for sure, because no written records exist. However, there are few available theories, proposed by various scientists, regarding the method that was applied by Eupalinos for the successful and with incredible precision completion of the tunnel that was excavated from both sides.

The first person to deal with the subject was the Greek engineer Heron of Alexandria (circa 70 AD). Efforts to explain the alignment method continued after the modern discovery of the monument in the 18th century.

A well thought method that explains the alignment question is given in the architectural and archaeological study the monument that was compiled by Dr. Hermann Kienast of the German Archaeological Institute of Greece. The initiative of this study has been of Ulf Jantzen former director of the institute. The study comprises of 213 pages of text, plus 41 pages of high quality photographs and drawings. Among others the study covers issues such as the monument’s investigation and discovery, the concept of its design and construction, the subsequent interventions, design, construction and functionality of the ancient works, mathematics and geometry of the tunnel alignment, the ancient marking and aligning systems, meeting point of excavations, geometrical design assumptions, geological conditions etc. His study is the only exact thorough work that exploits the issue describing and explaining the aqueduct of Eupalinos to the maximum possible detail.

Plan View: Kienast, 1995 &
Tokmakidis, 2009

Legend1. Agiades Spring2. The aqueduct as covered trench3. The qanat part 4. North portal of the main tunnel 5. Triangular deviation of the excavation6. Meeting point under Kastro mount 7. South portal of main tunnel 8. The qanat part towards the city9. The fountain10. Roman aqueduct11. Hellenistic gymnasium12. Hellenistic villa 13. Pythagoreion14. Port15. Ancient fortress (~6.430m in length)16. Holy Monastery Panagia Spiliani17. Holy Monastery of Zoodohos Pigi18. Ancient mines

Longitudinal Section: Tokmakidis, 2009

animation film

The Eupalinos Tunnel is considered as the first underground project excavated with a geometry-based approach. A simplified and animated presentation of the construction of the project and of the processes used was prepared by the ASSOCIATION of ANCIENT GREEK TECHNOLOGY STUDIES (EMAET) under the supervision of Prof. T. Tassios and can be viewed from the link on the right.

Measuring Instruments

Horizontal planks

Chorobates

ancient samos

Samos has been inhabited for more than 2½ thousand years. Samos flourished in the sixth century B.C. during the reign of the tyrant Polycrates (570–522 B.C.), whose court attracted poets, artists, musicians, philosophers, and mathematicians from all over the Greek world. It boasts the honour to be the birth place of some of the most famous ancient Greek philosophers and mathematicians such as Pythagoras, Aristarchus and Epicurus.

MONUMENT RESTORATION

A multi-discipline design study was carried out for restoration purposes since parts of the monument suffer stability problems. The study initiated in 2009, completed in 2011 and was conducted by a group of consultants which worked under the supervision of Egnatia Odos S.A. in cooperation with the Prefecture of Samos and the Ministry of Culture. The scope of the restoration studies was the rehabilitation of the monument, its protection against natural wear and the provision of safe conditions for public accessibility. The studies that were carried out focused in the main 1036m long tunnel and included definitive and implementation surveying, geophysical, geological, geotechnical, structural, electrical - mechanical and architectural works. For the execution of the works the Hellenic Ministry of Culture assigned a contract and currently the restoration works are under construction.

Engineering geological aspects

Eupalinos Aqueduct is not only a unique ancient monument and an astonishing pioneering achievement of engineering, but also a museum of the interaction between humankind and geological formations. The aqueduct was bored mainly through: (a) medium-bedded to massive limestones, (b) alternations between marls, shales and platy limestones, and (c) tectonic breccia. These geological formations are members of Hora and Pythagorion (volcano-) sedimentary sequences of Mytilinii molassic basin. This basin has formed during Miocene and Pliocene age.

Considering its age (~2.500 years) the aqueduct, and mainly the tunnel (which is the most significant structure) is preserved in a very good condition and it is accessible along its total length.

current monument status

The Greek Ministry of Culture in order to ensure safe conditions for the accessibility of the monument contacted a restoration study in 2011, which was approved by the Greek Central Archaeological Council. The restoration works that were designed, completed during mid 2017.

For more information regarding the operation of Eupalinos tunnel, please refer to the Ephorate of Antiquities of Samos-Ikaria or use this LINK.